reaches a climax state, yields can be controlled
and sustained indefinitely (9).

Ecological research in the 1970s and 1980s
revealed, however, that ecosystems are not in a
continual state of stable equilibrium. Rather, disturbances such as fire, wind, floods, and drought
are integral to maintaining healthy ecosystems
(10, 11). This shift in thinking implied that managing
ecosystems was more complex than extracting
predetermined sustainable yields. Disturbances are
necessary rather than harmful, viability of commercially relevant species depends on the whole
ecosystem, and populations vary spatially and temporally. In short, ecosystems function as complex,
dynamic systems with nonlinear responses to internal and external forces, feedbacks across space and
time, thresholds, and inherent unpredictability (12).

Another fundamental shift from the maximum-yield paradigm came from the realization that
human societies depend on ecosystems for well-being and services other than commodities. In
2005, the Millennium Ecosystem Assessment
called attention to the multiple services provided
by ecosystems, including provisioning (e.g., food),
regulating (e.g., water filtration and decomposition of wastes), supporting (e.g., soil formation),
and cultural services (e.g., recreation) (13). Ecosystems perform several functions simultaneously.
A forest can sequester carbon from the atmosphere,
provide habitat for biodiversity, constitute a sacred
and recreational space, and produce timber.

Awareness of human behavior and social in-stitutions as integral parts of ecosystems has alsobeen growing. For example, the spread of infec-tious disease depends on human behaviors, suchas contact with others, as well as population dy-namics of disease vectors. These interactions giverise to complex dynamics (14). Moreover, in a global-ized world, trade and exchanges between distantregions alter norms and rules of resource extrac-tion in increasingly unpredictable ways (15).

The realization that ecosystems behave as
complex systems, with humans as a component,
has upended the notion that managers can predictably obtain resources from ecosystems by
following simple formulas and exerting top-down
control. Problems in ecosystem management, such
as reducing mortality from infectious diseases (14)
and improving water quality affected by non–point
source pollutants (16), have proven to be much
less tractable than once thought.

Complexity gives rise
to wicked problems

Because ecosystems are inherently dynamic and
largely unpredictable complex systems, ecosystem
management is a “wicked problem” (17–19). The
concept of wicked problems arose more than

30 years ago in response to the dominance oftop-down, expert-driven technical and engineer-ing solutions to thorny issues in public policy,such as poverty alleviation and unemploymentin urban communities (20). Wicked problems areinherently resistant to clear definitions and easilyidentifiable, predefined solutions. In contrast, tameproblems, such as building an engineered struc-ture, are by definition solvable with technical solu-tions that apply equally in different places. Wickedproblems have been described in many disci-plines, including public health, political science,business management, urban and regional plan-ning, and natural resource management.

Rittel and Webber (19) have defined 10 primary characteristics of wicked problems, including the elusiveness of a final resolution, no
definitive test for a solution, and no generalizable
solution that applies in all cases. Wicked problems are seemingly intractable and subject to
multiple interpretations.

Heifetz (21) classified problems in terms of
their wickedness. Type I problems are technical
in nature and have clearly defined questions and
mechanical, straightforward solutions (i.e., they
are tame). Type II problems are clearly definable
but have no clear-cut solution. Solutions to type

II problems are only proposals that must be tested
and refined on the basis of outcomes. Type III
problems have neither clear-cut definitions nor
technical solutions. Type III problems are the most
wicked and require continual learning to formulate
the problem and adaptively work toward solutions.
In ecosystem management, researchers have
identified many types of wicked, non–type I problems (Table 1). Wicked problems arise from one
or a combination of multiple dimensions (20):
complexity and interdependency of components,
which create feedbacks and nonlinear responses
to management interventions; uncertainty of risks
and unintended consequences; divergence in values
and decision-making power of multiple stakeholders; and mismatches in spatial and temporal
scales of ecological and administrative processes.

Several realities of the 21st century make ecosystem
management an increasingly wicked problem.
For most of human history, ecosystems essentially
functioned as self-regulating adaptive systems with
self-organizing properties that evolved through
long-term interactions between populations and
their environments (12). Human societies benefited from these properties to obtain resources.
In the 21st century, humans have increasingly
used approaches that replace or supplement ecosystem functions—such as pesticides that replace
the ecological function of natural predators of
pest species and fertilizers that augment nutrient cycling, a fundamental role of ecosystems.
These approaches often do not mimic the self-regulating properties of ecosystems. The mismatch
gives rise to unintended consequences, such as
the loss of natural predators of pest species and
the accumulation of excess nutrients in waterways that receive runoff from fertilized fields. Such
human management has helped unprecedented
numbers of people to escape extreme poverty and